Low power tissue ablation system

ABSTRACT

Devices, systems and methods are disclosed for the ablation of tissue. Embodiments include an ablation catheter that has an array of ablation elements attached to a deployable carrier assembly. The carrier assembly can be constrained within the lumen of a catheter, and deployed to take on an expanded condition. The carrier assembly includes multiple electrodes that are configured to ablate tissue at low power. Additional embodiments include a system that includes an interface unit for delivering one or more forms of energy to the ablation catheter.

STATEMENT OF RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/698,355, filed Jul. 11, 2005, entitled “LowPower Tissue Ablation System”, which is incorporated by reference in itsentirety herein.

FIELD OF THE INVENTION

The present invention relates generally to systems, catheters andmethods for performing targeted tissue ablation in a subject. Inparticular, the present invention provides devices comprising one ormore elements designed to efficiently deliver energy to tissue withprecise control of the tissue to be ablated.

BACKGROUND OF THE INVENTION

Tissue ablation is used in numerous medical procedures to treat apatient. Ablation can be performed to remove undesired tissue such ascancer cells. Ablation procedures may also involve the modification ofthe tissue without removal, such as to stop electrical propagationthrough the tissue in patients with an arrhythmia. Often the ablation isperformed by passing energy, such as electrical energy, through one ormore electrodes causing the tissue in contact with the electrodes toheat up to an ablative temperature. Ablation procedures can be performedon patients with atrial fibrillation by ablating tissue in the heart.

Mammalian organ function typically occurs through the transmission ofelectrical impulses from one tissue to another. A disturbance of suchelectrical transmission may lead to organ malfunction. One particulararea where electrical impulse transmission is critical for proper organfunction is in the heart. Normal sinus rhythm of the heart begins withthe sinus node generating an electrical impulse that is propagateduniformly across the right and left atria to the atrioventricular node.Atrial contraction leads to the pumping of blood into the ventricles ina manner synchronous with the pulse.

Atrial fibrillation refers to a type of cardiac arrhythmia where thereis disorganized electrical conduction in the atria causing rapiduncoordinated contractions that result in ineffective pumping of bloodinto the ventricle and a lack of synchrony. During atrial fibrillation,the atrioventricular node receives electrical impulses from numerouslocations throughout the atria instead of only from the sinus node. Thiscondition overwhelms the atrioventricular node into producing anirregular and rapid heartbeat. As a result, blood pools in the atria andincreases the risk of blood clot formation. The major risk factors foratrial fibrillation include age, coronary artery disease, rheumaticheart disease, hypertension, diabetes, and thyrotoxicosis. Atrialfibrillation affects 7% of the population over age 65.

Atrial fibrillation treatment options are limited. Three knowntreatments, lifestyle change, medical therapy and electricalcardioversion all have significant limitations. Lifestyle change onlyassists individuals with lifestyle-related atrial fibrillation.Medication therapy assists only in the management of atrial fibrillationsymptoms, may present side effects more dangerous than atrialfibrillation, and fail to cure atrial fibrillation. Electricalcardioversion attempts to restore sinus rhythm but has a high recurrencerate. In addition, if there is a blood clot in the atria, cardioversionmay cause the clot to leave the heart and travel to the brain or to someother part of the body, which may lead to stroke. What are needed arenew methods for treating atrial fibrillation and other conditionsinvolving disorganized electrical conduction.

Various ablation techniques have been proposed to treat atrialfibrillation, including the Cox-Maze procedure, linear ablation ofvarious regions of the atrium, and circumferential ablation of pulmonaryvein ostia. The Cox-Maze procedure and linear ablation procedures areunrefined, unnecessarily complex, and imprecise, with unpredictable andinconsistent results and an unacceptable level of unsuccessfulprocedures. These procedures are also tedious and time-consuming, takingseveral hours to accomplish. Pulmonary vein ostial ablation is provingto be difficult to do, and has led to rapid stenosis and potentialocclusion of the pulmonary veins. There is therefore a need for improvedatrial ablation products and techniques.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an ablation system used byan operator to treat a patient is disclosed. The system comprises anablation catheter that has a flexible shaft with a proximal end and adistal end, and includes at least one ablation element for deliveringenergy to tissue. The system further comprises an interface unit thatprovides energy to the ablation catheter. The at least one ablationelement is configured to rapidly transition from a first temperature toa second temperature. The first temperature approaches tissue ablationtemperature, preferably 60° C., and the second temperature approachesbody temperature, typically 37° C. In a preferred embodiment, the atleast one ablation element has a majority of surface area in contactwith circulating blood when energy is being delivered to the tissue. Themajority of this blood exposed surface area is at least 60%, preferablymore than 75% and potentially greater than 85% of the total surface areaof the electrode. Numerous electrode configurations are describedincluding three segment (“triangle”), semicircular and crescent crosssections, cross sections with curvilinear, serpentine and zigzagsegments; cross sections with segments with projecting fins, and crosssections that include an energy delivery portion and a non-energydelivery portion. The electrodes of the present invention are configuredto rapidly cool, during energy delivery such as in bipolar energydelivery that follows monopolar energy delivery; and when no energy isbeing delivered. The electrodes of the present invention are configuredto transition from ablation temperature to body temperature in less than20 seconds, preferably less than 10 seconds. These electrodes are alsoconfigured to transition from body temperature to ablation temperaturein less than 5 seconds.

According to a second aspect of the invention, an ablation system usedby an operator to treat a patient is disclosed. The system comprises anablation catheter that has a flexible shaft with a proximal end and adistal end, and includes at least one ablation element for deliveringenergy to tissue. The system further comprises an interface unit thatprovides energy to the ablation catheter. The at least one ablationelement is configured such that a majority of its external surface areais in contact with tissue when energy is delivered to that tissue. Theelectrode is configured such that at least 60% of the total surface areais in tissue contact, preferably 70% or more. Numerous electrodeconfigurations are described including three segment (“triangle”),semicircular and crescent cross sections, cross sections withcurvilinear, serpentine and zigzag segments; cross sections withsegments with projecting fins, and cross sections that include an energydelivery portion and a non-energy delivery portion. The electrodes ofthe present invention are configured to maximize the amount of energytransferred to the tissue, thus minimizing the amount of energydelivered to the blood, such as undesired energy which may cause a bloodclot.

According to a third aspect of the invention, an ablation system used byan operator to treat a patient is disclosed. The system comprises afirst ablation catheter that has a flexible shaft with a proximal endand a distal end, and includes at least one ablation element fordelivering energy to tissue; and a second ablation catheter that has aflexible shaft with a proximal end and a distal end, and includes atleast one ablation element for delivering energy to tissue. The systemfurther comprises an interface unit that provides energy to the ablationcatheter. The energy delivered by the system is limited by a thresholdthat is a first value when the first ablation catheter is in use and adifferent value when the second ablation catheter is in use. The firstand second ablation catheters preferably include one or more differentfunctional elements, such as different ablation elements and/or patternsof ablation elements. Ablation elements can be varied in size and crosssectional geometry, cooling and heating properties, type of energydelivered, and other electrode parameters.

According to a fourth aspect of the invention, an ablation system usedby an operator to treat a patient is disclosed. The system comprises anablation catheter that has a flexible shaft with a proximal end and adistal end, and includes at least one ablation element for deliveringenergy to tissue. The system further comprises an interface unit thatprovides energy to the ablation catheter. The energy delivered by theinterface unit is configured to (1) achieve a target energy level t atarget tissue depth; and (2) pulse energy such that the tissuesurrounding the electrode does not exceed a threshold temperature. In apreferred embodiment, the energy delivered is RF energy, and the systemis configured to automatically transition between bipolar and monopolarRF delivery. Energy delivery is adjusted based on a value selected fromthe group consisting of: temperature of tissue; rate of change oftemperature of tissue; temperature of the at least one ablation element;rate of change of temperature of the at least one ablation element; EKG;tissue thickness; tissue location; cardiac flow rate; and combinationsthereof. Automatic adjustments are made to minimize depth of the lesion,minimize the width of the lesion, or both. In a preferred embodiment,the energy delivery is adjusted to achieve a target depth of the lesion.Temperature information is preferably provided by one or moretemperature sensors, such as sensors mounted in, on or near an ablationelement.

According to a fifth aspect of the invention, an ablation system used byan operator to treat a patient is disclosed. The system comprises anablation catheter that has a flexible shaft with a proximal end and adistal end, and includes at least one ablation element for deliveringenergy to tissue. The system further comprises an interface unit thatprovides energy to the ablation catheter. The interface unit monitorsone or more parameters of the system, and prevents the energy deliveredfrom exceeding a threshold. The value of the threshold is determined bythe at least one ablation element. The system parameters are preferablyselected from the group consisting of: temperature such as temperaturefrom a temperature sensor; a value of measured current; a value ofmeasured voltage; a flow measurement value; a force measurement valuesuch as a measurement of strain; a pressure measurement value; andcombinations thereof. The threshold is preferably an energy deliverythreshold selected from the group consisting of: peak energy such aspeak energy below 10 Watts; average energy such as average energy below5 Watts; and cumulative energy such as a value below 500 Watt-seconds orless than 300 Watt-seconds; and combinations thereof. In anotherpreferred embodiment, the interface unit includes a threshold comparatorfor comparing a measured, calculated or otherwise determined value tothe threshold. In another preferred embodiment, the threshold changesover time. In yet another preferred embodiment, the system is configuredto deliver a low level energy delivery followed by a higher level energydelivery. During or immediately following the low level energy delivery,a threshold value is determined which is utilized in the subsequenthigher level energy delivery.

According to a sixth aspect of the invention, an ablation catheterdevice is disclosed. The ablation catheter comprises an elongated,flexible, tubular body member having a proximal end, a distal end, and alumen extending therebetween. A control shaft is coaxially disposed andis slidingly received within the lumen of the tubular body member. Thecatheter further comprises a flexible carrier assembly which includes atleast two arms, each arm including at least one ablation element used todeliver energy to tissue. Each ablation element includes a relativelyuniform triangle cross-section along its length, with a continuous ordiscontinuous perimeter or path. The cross section is preferably anisosceles triangle wherein the common base is opposite two sides thatdetermine a vertex angle. This vertex angle is configured, based on thenumber of carrier arms of the particular carrier assembly, to allow anumber of electrodes to be constrained into a volumetrically efficientcircle or “pie” shape, the sum of all the vertex angles approximating360 degrees, such that:${{Vertex}\quad{Angle}} = \frac{360\quad{degrees}}{{Number}\quad{of}\quad{Carrier}\quad{Arms}}$

In an alternative embodiment, at least one cross section is dissimilar,and/or the cross sections do not include only isosceles trianglegeometries. In these configurations, the relevant (vertex) angles areconfigured such that their sum approaches 360 degrees in total,similarly providing efficiently constrainable volumes when maintainedwithin the lumen of carrier assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments of thepresent invention, and, together with the description, serve to explainthe principles of the invention. In the drawings:

FIG. 1 illustrates the treatment to be accomplished with the devices andmethods described below.

FIG. 2 a illustrates a perspective view of an ablation catheterconsistent with the present invention in which the carrier element hasfour carrier arms, each including two ablation elements.

FIG. 2 b is a sectional view of a finned electrode of FIG. 2 a.

FIG. 3 a is a sectional view of an ablation element consistent with thepresent invention.

FIG. 3 b is a sectional view of multiple ablation elements of FIG. 3 ashown constrained in the distal end of an ablation catheter of thepresent invention.

FIG. 3 c is a perspective, partial cutaway view of the ablation catheterof FIG. 3 b.

FIG. 4 illustrates a perspective, partial cutaway view of a preferredembodiment of an ablation catheter consistent with the present inventionin which the carrier element has three carrier arms each including twoablation elements.

FIG. 4 a is a sectional view of a distal portion of the ablationcatheter of FIG. 4.

FIGS. 5 a, 5 b, 5 c, 5 d, 5 e, and 5 f are sectional end views ofablation elements consistent with the present invention, shown inassociated contact with tissue during energy delivery.

FIGS. 6 a and 6 b are sectional end views of ablation elementsconsistent with the present invention.

FIG. 6 c is a side view of an ablation element consistent with thepresent invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention utilizes ablation therapy. Tissue ablation isoften used in treating several medical conditions, including abnormalheart rhythms. Ablation can be performed both surgically andnon-surgically. Non-surgical ablation is typically performed in aspecial lab called the electrophysiology (EP) laboratory. During thisnon-surgical procedure a catheter is inserted into a vessel such as avein, and guided into the heart using fluoroscopy for visualization.Subsequently, an energy delivery apparatus is used to supply energy tothe heart muscle. This energy either “disconnects” or “isolates” thepathway of the abnormal rhythm. It can also be used to disconnect theconductive pathway between the upper chambers (atria) and the lowerchambers (ventricles) of the heart. For individuals requiring heartsurgery, ablation can be performed during coronary artery bypass orvalve surgery.

The present invention provides catheters for performing targeted tissueablation in a subject. In preferred embodiments, the catheters comprisea tubular body member having a proximal end and distal end andpreferably a lumen extending therebetween. The catheter is preferably ofthe type used for performing intracardiac procedures, typically beingintroduced from the femoral vein in a patient's leg or a vein in thepatient's neck. The catheter is preferably introducible through a sheathwith a steerable tip that allows positioning of the distal portion to beused, for example, when the distal end of the catheter is within a heartchamber. The catheters include ablation elements mounted on a carrierassembly. The carrier assembly is preferably attached to a coupler,which in turn is connected to a control shaft that is coaxially disposedand slidingly received within the lumen of the tubular body member. Thecarrier assembly is deployable from the distal end of the tubular bodymember by advancing the control shaft, such as to engage one or moreablation elements against cardiac tissue, which is typically atrial walltissue or other endocardial tissue. Retraction of the control shaftcauses the carrier assembly to be constrained within the lumen of thetubular body member.

Arrays of ablation elements, preferably electrode arrays, may beconfigured in a wide variety of ways and patterns. In particular, thepresent invention provides devices with electrode arrays that provideelectrical energy, such as radiofrequency (RF) energy, in monopolar(unipolar), bipolar or combined monopolar-bipolar fashion, as well asmethods for treating conditions (e.g., atrial fibrillation, supraventricular tachycardia, atrial tachycardia, ventricular tachycardia,ventricular fibrillation, and the like) with these devices. Alternativeto or in combination with ablation elements that deliver electricalenergy to tissue, other forms and types of energy can be deliveredincluding but not limited to: sound energy such as acoustic energy andultrasound energy; electromagnetic energy such as electrical, magnetic,microwave and radiofrequency energies; thermal energy such as heat andcryogenic energies; chemical energy such as energy generated by deliveryof a drug; light energy such as infrared and visible light energies;mechanical and physical energy; radiation; and combinations thereof.

As described above, the normal functioning of the heart relies on properelectrical impulse generation and transmission. In certain heartdiseases (e.g., atrial fibrillation) proper electrical generation andtransmission are disrupted or are otherwise abnormal. In order toprevent improper impulse generation and transmission from causing anundesired condition, the ablation catheters of the present invention maybe employed.

One current method of treating cardiac arrhythmias is with catheterablation therapy, which, to date, has been difficult and impractical toemploy. In catheter ablation therapy, physicians make use of cathetersto gain access into interior regions of the body. Catheters withattached electrode arrays or other ablating devices are used to createlesions that disrupt electrical pathways in cardiac tissue. In thetreatment of cardiac arrhythmias, a specific area of cardiac tissuehaving aberrant conductive pathways, such as atrial rotors, emitting orconducting erratic electrical impulses, is initially localized. A user(e.g., a physician such as an electrophysiologist) directs a catheterthrough a main vein or artery into the interior region of the heart thatis to be treated. The ablating element is next placed near the targetedcardiac tissue that is to be ablated. The physician directs energy,provided by a source external to the patient, from one ore more ablationelements to ablate the neighboring tissue and form a lesion. In general,the goal of catheter ablation therapy is to disrupt the electricalpathways in cardiac tissue to stop the emission of and/or prevent thepropagation of erratic electric impulses, thereby curing the heart ofthe disorder. For treatment of atrial fibrillation, currently availablemethods and devices have shown only limited success and/or employdevices that are extremely difficult to use or otherwise impractical.

The ablation catheters of the present invention allow the generation oflesions of appropriate size and shape to treat conditions involvingdisorganized electrical conduction (e.g., atrial fibrillation). Theablation catheters of the present invention are also practical in termsof ease-of-use and limiting risk to the patient, as well assignificantly reducing procedure times. The present inventionaccomplishes these goals by, for example, the use of spiral shaped andradial arm shaped (also called umbrella shaped) carrier assemblies whoseablation elements create spiral, radial, or other simple or complexshaped patterns of lesions in the endocardial surface of the atria bydelivery of energy to tissue or other means. The lesions created by theablation catheters are suitable for inhibiting the propagation ofinappropriate electrical impulses in the heart for prevention ofreentrant arrhythmias.

Definitions. To facilitate an understanding of the invention, a numberof terms are defined below.

As used herein, the terms “subject” and “patient” refer to any animal,such as a mammal like livestock, pets, and preferably a human. Specificexamples of “subjects” and “patients” include, but are not limited, toindividuals requiring medical assistance, and in particular, requiringatrial fibrillation catheter ablation treatment.

As used herein, the terms “catheter ablation” or “ablation procedures”or “ablation therapy,” and like terms, refer to what is generally knownas tissue destruction procedures.

As used herein, the term “ablation element” refers to an energy deliveryelement, such as an electrode for delivering electrical energy. Ablationelements can be configured to deliver multiple types of energy, such asultrasound energy and cryogenic energy, either simultaneously orserially. Electrodes can be constructed of a conductive plate, wirecoil, or other means of conducting electrical energy through contactingtissue. In monopolar energy delivery, the energy is conducted from theelectrode, through the tissue to a ground pad, such as a conductive padattached to the back of the patient. The high concentration of energy atthe electrode site causes localized tissue ablation. In bipolar energydelivery, the energy is conducted from a first electrode to one or moreseparate electrodes, relatively local to the first electrode, throughthe tissue between the associated electrodes. Bipolar energy deliveryresults in more precise, shallow lesions while monopolar deliveryresults in deeper lesions. Both monopolar and bipolar delivery provideadvantages, and the combination of their use is a preferred embodimentof this application. Energy can also be delivered using pulse widthmodulated drive signals, well known to those of skill in the art. Energycan also be delivered in a closed loop fashion, such as a system withtemperature feedback wherein the temperature modifies the type,frequency and or magnitude of the energy delivered.

As used herein, the term “carrier assembly” refers to a flexiblecarrier, on which one or more ablation elements are disposed. Carrierassemblies are not limited to any particular size, or shape, and can beconfigured to be constrained within an appropriately sized lumen.

As used herein, the term “spiral tip” refers to a carrier assemblyconfigured in its fully expanded state into the shape of a spiral. Thespiral tip is not limited in the number of spirals it may contain.Examples include, but are not limited to, a wire tip body with onespiral, two spirals, ten spirals, and a half of a spiral. The spiralscan lie in a relatively single plane, or in multiple planes. A spiraltip may be configured for energy delivery during an ablation procedure.

As used herein the term “umbrella tip” refers to a carrier assembly witha geometric center which lies at a point along the axis of the distalportion of the tubular body member, with one or more bendable or hingedcarrier arms extending from the geometric center, in an umbrellaconfiguration. Each carrier arm may include one or more ablationelements. Each carrier arm of an umbrella tip includes a proximal armsegment and a distal arm segment, the distal arm segment more distalthan the proximal arm segment when the carrier assembly is in a fullyexpanded condition. One or more additional carrier arms can be includedwhich include no ablation elements, such as carrier arms used to providesupport or cause a particular deflection. An umbrella tip body is notlimited to any particular size. An umbrella tip may be configured forenergy delivery during an ablation procedure.

As used herein, the term “lesion,” or “ablation lesion,” and like terms,refers to tissue that has received ablation therapy. Examples include,but are not limited to, scars, scabs, dead tissue, burned tissue andtissue with conductive pathways that have been made highly resistive ordisconnected.

As used herein, the term “spiral lesion” refers to an ablation lesiondelivered through a spiral tip ablation catheter. Examples include, butare not limited to, lesions in the shape of a wide spiral, and a narrowspiral, a continuous spiral and a discontinuous spiral.

As used herein, the term “umbrella lesion” or “radial lesion,” and liketerms, refers to an ablation lesion delivered through an umbrella tipablation catheter. Examples include, but are not limited to, lesionswith five equilateral prongs extending from center point, lesions withfour equilateral prongs extending from center point, lesions with threeequilateral prongs extending from center point, and lesions with threeto five non-equilateral prongs extending from center point.

As used herein, the term “coupler” refers to an element that connectsthe carrier assembly to the control shaft. Multiple shafts, or ends ofthe carrier assembly may connect to the coupler. Multiple carrier armscan have one or more of their ends attached to the coupler. The couplermay include anti-rotation means that work in combination with matingmeans in the tubular body member. Couplers may be constructed of one ormore materials such as polyurethane, steel, titanium, and polyethylene.

As used herein, the term “carrier arm” refers to a wire-like shaftcapable of interfacing with electrodes and the coupler. A carrier arm isnot limited to any size or measurement. Examples include, but are notlimited to: stainless steel shafts; Nitinol shafts; titanium shafts;polyurethane shafts; nylon shafts; and steel shafts. Carrier arms can beentirely flexible, or may include flexible and rigid segments.

As used herein, the term “carrier arm bend point” refers to a joint(e.g., junction, flexion point) located on a carrier arm. The degree offlexion for a carrier arm bend point may range from 0 to 360 degrees.The bend portion can be manufactured such that when the carrier assemblyis fully expanded, the bend point is positioned in a relatively straightconfiguration, a curved configuration, or in a discrete transition froma first direction to a second direction, such as a 45 degree bendtransition. The bend portion can include one or more flexing means suchas a spring, a reduced diameter segment, or a segment of increasedflexibility.

The present invention provides structures that embody aspects of theablation catheter. The present invention also provides tissue ablationsystems and methods for using such ablation systems. The illustrated andvarious embodiments of the present invention present these structuresand techniques in the context of catheter-based cardiac ablation. Thesestructures, systems, and techniques are well suited for use in the fieldof cardiac ablation.

However, it should be appreciated that the present invention is alsoapplicable for use in other tissue ablation applications such as tumorablation procedures. For example, the various aspects of the inventionhave application in procedures for ablating tissue in the prostrate,brain, gall bladder, uterus, and other regions of the body, preferablyregions with an accessible wall or flat tissue surface, using systemsthat are not necessarily catheter-based.

The multifunctional catheters of the present invention have numerousadvantages over previous prior art devices. The present inventionachieves efficiency in tissue ablation by maximizing contact betweenelectrodes and tissue, such as the atrial walls, while also achievingrapid and/or efficient transfer of heat from the electrode into thecirculating blood (“cooling”), such as by maximizing electrode surfacearea in contact with circulating blood. To achieve this result, in apreferred embodiment the electrode has a projecting fin that isconfigured to act as a heat sink that provides rapid and efficientcooling of the electrode. In another preferred embodiment the electrodecomprises two components such that one component, the electrodeconductive portion, contracts tissue and the other component, thenonconductive portion, remains thermally conductive. The presentinvention includes electrodes with improved and miniaturized crosssectional geometries and carrier assemblies that “fold-up” efficientlyto allow a smaller ablation catheter to be employed. These improvedelectrodes are preferably triangularly shaped as described in detail inreference to subsequent figures below. Because these triangularelectrodes fold up efficiently, and can have either a “base” to contacttissue or a “point” to contact tissue, greater efficiency andversatility are achieved. The devices and systems are configured tominimize the amount of tissue ablated while still achieving the desiredtherapeutic benefit of the ablation therapy. Ablated lesions are createdwith a target depth, and minimal widths. System components monitorenergy delivered, parameters associated with energy delivered and othersystem parameters. Energy delivered is prevented from achieving one ormore threshold values.

FIGS. 1-12 show various embodiments of the multifunctional catheters ofthe present invention. The present invention is not limited to theseparticular configurations.

FIG. 1 illustrates the treatment to be accomplished with the devices andmethods described herebelow. FIG. 1 shows a cutaway view of the humanheart 1 showing the major structures of the heart including the rightatrium 2, the left atrium 3, the right ventricle 4, and the leftventricle 5. The atrial septum 6 separates the left and right atria. Thefossa ovalis 7 is a small depression in the atrial septum that may beused as an access pathway to the left atrium from the right atrium. Thefossa ovalis 7 can be punctured, and easily reseals and heals afterprocedure completion. In a patient suffering from atrial fibrillation,aberrant electrically conducive tissue may be found in the atrial walls8 and 9, as well as in the pulmonary veins 10 and the pulmonary arteries11. Ablation of these areas, referred to arrhythmogenic foci (alsoreferred to as drivers or rotors), is an effective treatment for atrialfibrillation. Though circumferential ablation of the pulmonary veinusually cures the arrhythmia that originates in the pulmonary veins, asa sole therapy it is usually associated with lesions that have high riskof the eventual stenosis of these pulmonary veins, a very undesirablecondition. The catheters of the present invention provide means ofcreating lesions remote from these pulmonary veins and their ostia whileeasily being deployed to ablate the driver and rotor tissue.

To accomplish this, catheter 100 is inserted into the right atrium 2,preferably through the inferior vena cava 20, as shown in theillustration, or through the superior vena cava 21. Catheter 100 mayinclude an integral sheath, such as a tip deflecting sheath, or may workin combination with a separate sheath. When passing into the leftatrium, the catheter passes through or penetrates the fossa ovalis 7,such as over a guide wire placed by a trans-septal puncture device. Thecatheter 100 carries a structure carrying multiple ablation elementssuch as RF electrodes, carrier assembly 120, into the left atrium.Carrier assembly 120, which includes multiple electrodes 130, can beadvanced and retracted out of distal end of catheter 100. Carrierassembly 120 is adapted to be deformable such that pressing carrierassembly 120 into left atrial wall 9 will cause one or more, andpreferably all of electrodes 130 to make contact with tissue to beanalyzed and/or ablated. Each of the electrodes 130 is attached viaconnecting wires to an energy delivery apparatus, RF delivery unit 200,which is also attached to patch electrode 25, preferably a conductivepad attached to the back of the patient.

RF delivery unit 200 is configured to deliver RF energy in monopolar,bipolar or combination monopolar-bipolar energy delivery modes. In apreferred embodiment, monopolar energy delivery is followed by bipolarenergy delivery. In an alternative embodiment, the bipolar energy isthen followed by a period without energy delivery; such as a sequence inwhich the three steps are have equal durations. In another preferredembodiment, RF delivery unit 200 is configured to also provideelectrical mapping of the tissue that is contacted by one or moreelectrodes integral to carrier assembly 120. Electrodes 130, preferablywith a triangular cross section, can also be configured to be mappingelectrodes and/or additional electrodes can be integral to carrierassembly 120 to provide a mapping function. Carrier assembly 120 isconfigured to be engaged over an endocardial surface to map and/orablate tissue on the surface. RF energy is delivered after a properlocation of the electrodes 130 is confirmed with a mapping procedure. Ifthe position is determined to be inadequate, carrier assembly 120 isrepositioned through various manipulations at the proximal end of theablation catheter 100. In another preferred embodiment, RF delivery unit200 is configured to deliver both RF energy and ultrasound energythrough identical or different electrodes 130. In another preferredembodiment, RF delivery unit 200 is configured to accept a signal fromone or more sensors integral to ablation catheter 100, not shown, suchthat the energy delivered can be modified via an algorithm whichprocesses the information received from the one or more sensors. Theimproved electrodes and other catheter and system components of thepresent invention typically require only 3 to 5 watts of RF energy toadequately ablate the tissue. The minimal power requirements results inreduced procedure time as well as greatly enhanced safety of the overallprocedure.

FIGS. 2 a and 2 b illustrate an exemplary embodiment of the ablationcatheter 100 of the present invention. These ablation catheters havetriangular electrodes 130, each with fin 133 configured to provide rapidand efficient cooling of electrode 130. The cooling efficiency preventsover-heating of the electrode and neighboring tissue during ablation, aswell as a short transition time from an ablation temperature, preferably60° C., to body temperature, typically 37° C. after an ablation cyclehas ceased. This rapid transition is typically less than 20 seconds,even when the electrode remains in contact with recently ablated tissue.Other benefits of the rapid and efficient cooling electrodeconfiguration include reducing the risk of blood clotting.

The ablation elements of the present invention include RF energydelivery electrodes 130 of FIGS. 2 a and 2 b, as well as other elementscapable of delivering one or more forms of energy, described in detailhereabove, the electrodes and other system components configured in amanner sufficient to controllably ablate tissue. Electrodes 130 includeconductive materials, such as a metal or metal-coated material. Metalsand combinations of metals are appropriate such as: platinum, iridium,gold, stainless steel and aluminum. Conductive polymers are alsoappropriate materials. Conductive surfaces may be painted, coated orplated surfaces, such as gold plated over a copper base. Electrodematerials may also include foils such as aluminum or gold foils attachedto a base. Electrodes 130 deliver RF energy in monopolar or bipolar modeas has been described in reference to FIG. 1. Electrodes 130 aredesigned to have small surface area, typically less than 2.5 mm² andpreferably approximating 0.56 mm². Electrodes 130 are designed to havesmall volume, typically less than 3.0 mm³ and preferably approximating1.3 mm³. Electrodes 130 are designed to have small mass, typically lessthan 0.05 grams, and preferably approximating 0.03 grams. Theseminiaturized electrodes, especially those with a triangular crosssection, provide numerous advantages such as high ratio of energy tosurface area (energy density) during ablation, as well as efficientlycompact volume of carrier assembly 120 when constrained within the lumenof the ablation catheter in the retracted, undeployed state.

FIG. 2 a shows the structures of the ablation carrier assembly 120 andother portions of ablation catheter 100. The ablation carrier assembly120 shown includes carrier arms 123 that extend radially out from thecentral axis of the distal end of catheter shaft 101, the carrier arms123 positioned in a symmetric configuration with equal angles (ninetydegrees in a four arm configuration between each arm). Carrier assembly120 is shown with four carrier arms 123, however any number can be used,and each arm can carry one or more mapping or ablating electrodes 130,or be void of electrodes. Carrier arms 123 are resiliently biased,preferably constructed of a wire such as a ribbon wire, and may havesegments with different levels of flexibility. Carrier arms 123 areshown with multiple electrodes 130 fixedly mounted (such as with glues,soldering, welding, crimping or other attachment means) to its distalarm segment 127. In an alternative embodiment, different patterns ofelectrodes are employed, and one or more arms may be void of electrodessuch as where carrier arm 123 provides support only. In a preferredembodiment, different types of ablation elements are mounted to one ormore carrier arms 123, such as electrodes with different geometries, orablation elements that deliver different forms of energy. Carrier arms123 may also include mapping electrodes, thermal sensors or othersensors, with or without the inclusion of ablation elements. In apreferred embodiment, each carrier arm 123 includes at least oneablation element. In alternative embodiments, three or more arms can beseparated by non-equal angles.

Each carrier arm 123 includes proximal arm segment 125 and distal armsegment 127. Electrodes 130 are mounted onto distal arm segment 127.During the ablation procedure, an operator presses distal arm segment127 into tissue prior to and during energy delivery. Carrier assembly120 is configured with specific rigidity such that the operator canexert a nominal force to cause the appropriate electrodes 130 to pressand slightly “bury” into the tissue, without perforating or otherwisedamaging the neighboring tissue. In a preferred embodiment, the distalarm segments contain thermocouples such as sensors embedded in theelectrodes 130, or sensors mounted equidistant between two electrodes130. Proximal arm segment 125 and distal arm segment 127 connect at abendable joint, carrier arm bend point 121. In a preferred embodiment,proximal arm segment 125, distal arm segment 127 and bend point 121 area continuous resiliently flexible wire. Each distal arm segment 127bends radially inward from the bend point 121 toward the longitudinalaxis of catheter shaft 101. The distal arm segments 127 are shown alsoto tend proximally, to establish an acute angle with the proximal armsegment 125 from which it extends, and the angle is small such that thedistal end of the distal arm segment 127 is proximal to the carrier armbend point 121. Bend point 121 allows “folding out” of carrier assembly120 during retraction, acting as a hinge in providing the means forrotably joining the distal arm segment 127 to the proximal arm segment125. The proximal arm segment 125 of the carrier arm 123 may includetemperature sensors, not shown, such as thermocouples to measuretemperature of blood. In the configuration shown, the proximal armsegment 125 will not contact tissue during the ablation procedure. In analternative embodiment, proximal arm segment 125 includes one or moreelectrodes, for ablation and/or for mapping, such that the opposite sideof carrier assembly 120 can be used to map or ablate tissue and isconfigured to contact tissue, such as when carrier assembly 120 isdeployed and catheter shaft 101 is in tension such as when pulled backby an operator.

Each distal arm segment 127 connects, at its end opposite bend point121, to connection point 124, a mechanical joint such as a soldered,crimped or welded connection that stabilizes each distal arm segment 127relative to the others. In a preferred embodiment, two continuous wiresor ribbons are used to create the four distal arm segments 127. Eachwire or ribbon comprises the pair of distal arm segments 127 that arelinearly aligned, and the two wires are connected at their midpoint atconnection point 124. These wires or ribbons are preferably constructedof Nitinol, but other materials such as stainless steel or a plastic maybe used. In an alternative embodiment, the two connection wires areresiliently biased to deploy in the configuration shown in FIG. 2 a, butdo not include connection point 124 such that the center portion of thetwo continuous wires can move relative to each other.

Referring to the ablation catheter 100 structures, FIG. 2 a shows atubular body member that is an elongated, flexible, hollow tube,catheter shaft 101, which connects at its proximal end to handle 110.The material used for the construction of the catheter shaft 101 andeach component which resides or is configured to be inserted through alumen integral to catheter shaft 101, are selected to provide thesuitable flexibility, column strength and steerability to allowpercutaneous introduction of ablation catheter 100 through thevasculature of the patient, entering the right atrium 2 through theseptum 6 and into the left atrium 3. Catheter shaft 101 and othertubular conduits of ablation catheter 100 are constructed of materialssuch as Pebax, urethanes, nylons, thermoplastic elastomers, andpolyimides. The shafts may be reinforced with wire or plastic braidsand/or may include coil springs. Catheter shaft 101 is typically between4 to 12 French and typically 6 to 8 French. In a preferred embodiment,catheter shaft 101 is introduced through a deflectable sheath where thesheath mechanism is already in place in left atrium 3. In an alternativeembodiment, catheter 100 is inserted directly without the use of anouter sheath, and catheter 100 includes a deflectable tip assembly anddeflection controls.

Handle 110 on the ablation catheter includes controls to operate thecarrier assembly 120. Handle 110 is constructed of a rigid or semi-rigidmaterial such as Delrin or polycarbonate, and includes button 116 thatis connected to switch means, not shown, for starting and/or stoppingthe delivery of energy to one or more of electrodes 130. Handle 110 mayinclude other controls, not shown, to perform numerous functions such aschange energy delivery settings. Handle 110 may include a retractionmechanism, not shown, to advance and retreat carrier assembly 120. In analternative embodiment, handle 110 is attached to an inner shaftslidingly received within catheter shaft 101 such that retraction of thehandle 110 causes the carrier assembly 120 to collapse and beconstrained within the lumen at end of catheter shaft 101. Carrier arm123 is resiliently biased in shown position so that it can be collapsedand withdrawn within lumen of catheter shaft 101 through manipulation ofhandle 110 on proximal end of catheter 100.

Handle 110 includes a plug 118 that attaches to an interface unit of thepresent invention, such as an RF energy generator that also includesmapping functions and display. Plug 118 is connected to electrical wiresthat extend distally with a lumen integral to catheter shaft 101 ofcarrier assembly 120, terminating at each of the electrodes 130.

FIG. 2 b illustrates the cross section, preferably a uniform crosssection, of one or more electrodes 130 mounted to distal arm segment 127of FIG. 2 a. A projecting member, fin 133, assists in the rapid andefficient cooling of electrode 130 during and after ablation energyapplication, acting as a heat sink and efficiently transferring heatenergy to the neighboring blood, such as blood circulating in the leftatrium 3 or the right atrium 2 depending upon where the carrier assembly120 has been placed by the operator. The size, surface area and mass offin 133 are chosen to effectively transfer the heat energy whileallowing carrier assembly 120 to achieve a sufficiently compactconfiguration when constrained within the lumen of the ablationcatheter. In a preferred embodiment, fin 133 is sized such that theportion of the surface area of electrode 130 that is in contact withcirculating blood is at least 60%, and preferably 70% of the totalsurface area of electrode 130. Fin 133 may change laminar and/or othernon-turbulent flows to turbulent flow, such that heat is moreefficiently transmitted away from electrode 130. In an alternativeembodiment, illustrated and described in reference to FIGS. 5 c and 5 d,fin 133 may be electrically isolated from the remainder of electrode130, such that fin 133 does not deliver energy to the circulating blood.In another alternative embodiment, illustrated and described inreference to FIG. 6 b, electrode 130 may include multiple fins.

First wire 134 is an energy delivery conduit that connects to electrode130 to transfer ablation energy and preferably to also send and/orreceive signals to map the tissue of the heart. Second wire 135 depictsan exemplary wire that connects to electrode 130, and may act as thereturn wire to first wire 134, for return of ablation energy and/ormapping signals. Wire 134 and wire 135 are typically 30 awg wireincluding a 0.003″ polyamide insulating outer jacket, each parameterchosen to carry sufficient ablation currents and prevent voltagebreakdown between neighboring wires. The efficiency of the electrodes ofthe present invention, as well as the efficient configuration of theother components of the system, allow greatly reduced wire gauge andinsulation thickness, correlating to smaller diameter and more flexibleablation catheters.

Surface 136 is the base of the electrode that is the part of thestructure that contacts tissue during ablation. In a preferredembodiment, surface 136 is a small surface area so that energy deliveredper square area is maximized. Fin 133 projects from the apex oppositesurface 136, and provides sufficient surface area such that the majorityof the surface area of electrode 130 resides in the circulating bloodwhen surface 136 is in contact with tissue and energy is beingdelivered. Within the triangular cross section of electrode 130 passeseach wire 134 and 135, as well as distal arm segment 127, to whichelectrode 130 is fixedly mounted.

Referring now to FIGS. 3 a through 3 c, another preferred embodiment ofthe ablation catheter and components of the ablation system of thepresent invention is illustrated. Electrodes 130 have a triangular crosssection with a continuous perimeter or path, preferably an isoscelestriangle wherein the common base is opposite two sides that determine avertex angle. This vertex angle is configured, based on the number ofcarrier arms of the particular carrier assembly, to allow a number ofelectrodes to be constrained into a volumetrically efficient circle or“pie” shape, the sum of all the vertex angles approximating 360 degrees,such that:${{Vertex}\quad{Angle}} = \frac{360\quad{degrees}}{{Number}\quad{of}\quad{Carrier}\quad{Arms}}$

In an alternative embodiment, the cross sections are dissimilar, and/orthe cross sections do not include only isosceles geometries, however theindividual vertex angles are configured such that their sum approaches360 degrees in total, providing efficient constrained volume of thecarrier assembly. In addition to allowing compact constrained volume,and overall small surface area, volume and mass of electrodes 130, theelectrodes of the present invention provide maximum flexibility inperforming ablation procedures, such as by: minimizing energy deliveredto blood; avoiding energy delivered to non-targeted tissue and/orminimizing tissue area receiving energy during ablation; maximizingenergy density delivered to tissue; reducing procedure time, and otheradvantages. In a preferred embodiment, the ablation catheter and systemof the present invention includes multiple dissimilar electrodes,fixedly mounted to a single ablation catheter or mounted to multipleablation catheters used sequentially or simultaneously in a singleablation procedure for a patient.

Referring specifically to FIG. 3 a, electrode 130 a is configured todeliver RF energy to tissue via surface 136. Electrode 130 a of FIG. 3 ais similar to electrode 130 of FIG. 2 b with a smaller projecting fin133, sized to allow a more compact constrained configuration of thecarrier assembly while still increasing the surface area of electrode130 a in the circulating blood during ablation. Electrode 130 a isfixedly mounted to distal arm segment 127 which comprises a Nitinol wireor ribbon but alternatively a non-conductive material such as nylon orother non-metal which does not require electrode 130 a from beingelectrically isolated from distal arm segment 27, isolation means notshown. Electrode 130 a includes within its triangular cross section wire134 and wire 135 that are electrically connected to electrode 140 a andtravel proximally to an electrical connection point that attaches to aninterface unit of the present invention. Wire 134 and 135 provide supplyand return of RF power and potentially supply and return of mappingdrive and record signals. Additional wires and other energy delivery orother conduits, not shown, may pass through the triangular cross sectionof electrode 130 a, such as energy and/or signal delivery conduits thatconnect to sensors such as thermocouples, or other ablation or mappingelements. In a preferred embodiment, electrode 130 a includes anembedded thermocouple, not shown but preferably a bimetallicthermocouple consisting of copper and alloy 11 or Constantan alloy. Eachthermocouple is attached to 40 awg wire with a 0.001″ insulating jacket,the wires traveling proximally and attaching to the interface unit ofthe present invention for converting signals to temperature values.

Referring to FIG. 3 b, a partial cutaway view of the ablation catheterof the present invention is illustrated, including the multipleelectrodes 130 a of FIG. 3 a constrained with a lumen of catheter shaft101 of ablation catheter 100. Ablation catheter 100 may be configured tobe inserted through a deflectable guide catheter, or include distal tipdeflection means, not shown. Electrodes 130 a are fixedly mounted todistal arm segments 127 which are attached to proximal arm segments viaa bendable portion (both proximal arm segments and bendable portion notshown but described in detail in reference to FIG. 2 a). The ablationelement carrier assembly has been folded into the retracted state shown,by retraction of handle 110 and/or activation of a control of handle110, not shown but preferably a sliding knob or lever on handle 110.Handle 110 includes connector 118 for electrical attachment to an energydelivery apparatus such as an RF generator and/or electrophysiologymapping unit, and further includes button 116 used by the operator toinitiate an energy delivery event. Handle 110 may additionally includeother functional components and assemblies such as other control oractivation means, as well as audio and/or tactile transducers to alertthe operator of alert conditions.

Referring additionally to FIG. 3 c, the carrier assembly of FIGS. 3 band 3 c includes five electrodes 130 a and five distal arm segments 127that have been placed in a constrained condition within a lumen ofcatheter shaft 101 such that at least a portion of each of the trianglecross section of the five electrodes 130 a lie in a single plane. Eachelectrode 130 a has a similar isosceles triangle shaped cross sectionsuch that the vertex angle A approximates 75 degrees allowing thecompact 360 circular or pie shaped configuration. In the constrainedconfiguration shown, each vertex angle A is aligned radially outwardfrom the central axis of shaft 101 such that the tissue contactingsurface 136 of each electrode 130 a is in relative contact with theinner wall of shaft 101. These triangle cross sections and relativelysmall projecting fins 133 are sized and configured to allow a compactconstrained configuration that includes coupler 140 at its center.Coupler 140, described in detail in reference to FIG. 4, couples thecarrier arms of the carrier assembly to a slidable shaft, not shown butoperably attached to handle 110 and advanced and retracted by anoperator to position the carrier assembly in its deployed (expanded) andconstrained configurations respectively.

While the carrier assembly configuration of FIGS. 3 b and 3 c illustratea five carrier arm configuration that correlates to an electrode 130 across section triangular vertex angle approximating 75 degrees, it canbe easily derived from the equation above that a vertex angle of 120degrees would correspond to three arm carrier assembly configurationsand a vertex angle of 90 degrees would correspond to four armconfigurations. It also should be easily understood that in embodimentsin which electrode 130 a cross sections are dissimilar, the sum of thevertex angles of the appropriate cross sections, those cross sectionsthat are linearly aligned within the lumen of catheter shaft 101 in theretracted position, should approximate 360 degrees to minimize theoverall constrained cross sectional area.X

Referring now to FIGS. 4 and 4 a, another preferred embodiment ofablation catheter 100 and ablation system of the present invention isillustrated. Catheter 100 includes carrier assembly 120 configured inanother umbrella tip configuration. Carrier assembly 120 includes threecarrier arms 123, each separated by 120 degrees from the neighboring armwhen in the deployed condition, and each of which includes two ablationelements, electrodes 130. In an alternative embodiment, differentpatterns of electrodes are employed, and one or more arms may be void ofelectrodes. Electrodes can take on one or more various forms, such asthose described in detail in reference to FIGS. 5 a through 5 f andFIGS. 6 a through 6 c. The six electrodes 130 shown may have similar ordissimilar characteristics. They may be chosen to maximize cooling ormaximize energy delivery to tissue. Each electrode 130 may be energizedwith one or more forms of energy such as RF energy in a sequence ofmonopolar and bipolar energy delivery. Referring back to FIG. 4, carrierarms 123 extend radially out from the central axis of the distal end ofcatheter shaft 101. Each carrier arm 123 includes proximal arm segment125 and distal arm segment 127, these segments connected at a bendablejoint, bend point 121. In a preferred embodiment, proximal arm segment125 and distal arm segment 127 and bend point 121 are a continuousresiliently flexible wire, such as a “trained” Nitinol wire that createsthe umbrella tip. Each electrode 130 is mounted to an insulator,insulating band 131 such that the electrode is electrically isolatedfrom the wire segments of carrier assembly 120. Each electrode 130 isconnected to wires that extend along shafts of carrier assembly 120,toward a lumen of catheter shaft 101, and proximally to handle 110.These wires, not shown but described in detail hereabove, includeinsulation to electrically isolate one wire from another. One end ofeach distal arm segment 127 is attached to a cylinder, coupler 140,which is sized to be slidably received within a lumen of catheter shaft101.

Coupler 140 can be flexible or rigid, and may contain both rigid andflexible portions along its length. Coupler 140 may provide electricalconnection means to connect wires extending from the handle to wiresfrom carrier assembly 120 electrodes. The ends of the distal armsegments 127 and the ends of the proximal arm segments 125 can beattached to the outside of coupler 140, the inside of coupler 140 orboth. Coupler 140 includes along its outer surface, a projection,projection 142, which has a cross section profile which mates with arecess, groove 106 of catheter shaft 101 which prevents undesiredrotation of carrier assembly 120. In an alternative embodiment, cathetershaft 101 includes a projection, and coupler 140 includes a groove toaccomplish a similar prevention of rotation. In another alternativeembodiment, control shaft 150, which is slidingly received within alumen of shaft 101, additionally or alternatively includes a projectionor other means to mate with shaft 101 to prevent undesired rotation ofcarrier assembly 120. As depicted in FIG. 4 a, control shaft 140includes a thru lumen, lumen 152, such that ablation catheter 101 can beinserted over a guidewire (guidewire exit on handle 110 not shown).Additionally or alternatively, lumen 152 may include one or more wiresor other filamentous conduits extending from proximal handle 110 a pointmore distal.

Control shaft 150 is mechanically attached to coupler 140. Control shaft150 extends proximally to handle 110 and is operably connected to knob115 such that rotation of knob 115 from a deployed position to awithdrawn position causes carrier assembly 120 to be constrained withina lumen of catheter shaft 101, and rotation of knob 115 from a withdrawnposition to a deployed position causes carrier assembly 120 to extendbeyond the distal end of catheter shaft 101 to be in an expandedcondition. In a preferred embodiment, knob 115 is operably connected tocontrol shaft 150 via a cam, or set of gears, not shown, to provide amechanical advantage in the distance traveled by control shaft 150.

Catheter shaft 101 is preferably part of a steerable sheath, steeringmechanism not shown, and includes flush port 170, which is configured tobe attachable to a flushing syringe, used to flush blood and otherdebris or contaminants from the lumen of an empty catheter shaft 101(wherein control shaft 150, coupler 140 and carrier assembly 120 havebeen removed) or for flushing the space between control shaft 150 andthe inner wall of catheter shaft 101. Catheter shaft 101 is notconnected to handle 110, such that handle 110 can be withdrawn, removingcontrol shaft 150, coupler 140 and carrier assembly 120 from cathetershaft 101. This configuration is useful when these components areprovided in a kit form, including combinations of different versions ofthese components, the different combinations made available to treatmultiple patients, or a single patient requiring multiple electrodepatterns or other varied electrode properties such as tissue contactsurface area, electrode cooling properties and temperature sensorlocation. A preferred example of a kit would include the catheter shaft101 and flush port 170 of FIG. 6 acting as a sheath; kitted with theinsertable shaft assembly comprising handle 110, control shaft 150,coupler 140 and umbrella tipped carrier assembly 120 of FIG. 6 as wellas a second insertable shaft assembly. The second insertable shaftassembly preferably includes a different carrier assembly of ablationelements such as a different pattern of electrodes or electrodes withdifferent properties that the first insertable shaft assembly. Electrodeor other ablation element variations include but are not limited to:type of energy delivered; size; cross sectional geometry; coolingproperties; heating properties; and combinations thereof. In anotherpreferred embodiment of the kit, a catheter configured for creatinglesions at or near the pulmonary veins of the left atrium is included.

Also depicted in FIG. 4 is a system of the present invention, includingin addition to ablation catheter 100, RF delivery unit 200, an interfaceunit of the present invention which connects to handle 110 with amulti-conductor cable 202 at RF attachment port 181. RF delivery unit200 includes user interface 201, such as a user interface including datainput devices like touch screens, buttons, switches, keypads, magneticreaders and other input devices; and also including data output deviceslike data and image screens, lights, audible transducers, tactiletransducers and other output devices. User interface 201 is used toperform numerous functions including but not limited to: selectingelectrodes to receive energy (electrodes 130 of carrier assembly 120);setting power levels, types (bipolar and monopolar) and durations;setting catheter and other system threshold levels; setting mapping andother system parameters; initiating and ceasing power delivery;deactivating an alarm condition; and performing other functions commonto electronic medical devices. User interface 201 also providesinformation to the operator including but not limited to: systemparameter information including threshold information; mapping andablation information including ablation element temperature and coolinginformation; and other data common to ablation therapy and otherelectronic medical devices and procedures. In a preferred embodiment, RFdelivery unit 200 attaches to a temperature probe, such as an esophagealtemperature probe, determines the temperature from one or more sensorsintegral to the probe, and further interprets and/or displays thetemperature information on user interface 201. In another preferredembodiment, RF delivery unit 200 also includes cardiac mapping means,such that mapping attachment port 182 can be attached to RF deliveryunit 200 avoiding the need for a separate piece of equipment in thesystem. In another preferred embodiment, RF delivery unit 200 can alsodeliver ultrasound and/or another form of energy, such energy deliveredby one or more additional ablation elements integral to carrier assembly120, additional ablation elements not shown. Applicable types of energyinclude but are not limited to: sound energy such as acoustic energy andultrasound energy; electromagnetic energy such as electrical, magnetic,microwave and radiofrequency energies; thermal energy such as heat andcryogenic energies; chemical energy; light energy such as infrared andvisible light energies; mechanical energy; radiation; and combinationsthereof.

In a preferred embodiment, ablation catheter 100 includes an embeddedidentifier (ID), an uploadable electronic or other code, which can beused by RF delivery unit 200 to confirm compatibility and otheracceptability of the specific catheter 100 with the specific RF deliveryunit 200. The electronic code can be a bar code, not shown, on handle110 which is read by RF delivery unit 200, an electronic code which istransferred to RF delivery unit 200 via a wired or wireless connection,not shown, or other identifying means, such as an RF tag embedded inhandle 110. In another preferred embodiment, RF delivery unit 200 alsoincludes an embedded ID, such as an ID that can be downloaded tocatheter 100 for a second or alternative acceptability check. Theembedded ID can also be used to automatically set certain parameters orcertain parameter ranges, and can be used to increase safety bypreventing inadvertent settings outside of an acceptable range for thespecific catheter 100.

Handle 110 includes two push buttons, first button 116 and second button117. These buttons can be used to perform one or more functions, and canwork in cooperation with user input components of user interface 201such that commands entered into user interface 201 set the action takenwhen either or both button 116 and button 117 are pressed. In apreferred embodiment, both button 116 and button 117 must be pressedsimultaneously to deliver energy to one or more ablation elements ofcatheter 100. At the distal end of catheter shaft 101 is acircumferential band, band 104. Band 104 is preferably a visualizationmarker, such as a radiographic marker, ultrasound marker,electromagnetic marker, magnetic marker and combinations thereof. In analternative embodiment, band 104 transmits or receives energy, such aswhen the marker is used as a ground or other electrode during anablation. In another alternative embodiment, band 104 is an antenna usedto determine the position of the distal end of catheter shaft 101 or thelocation of another component in relation to band 104. In anotherpreferred embodiment, band 104 is used to store energy, such ascapacitively stored energy that can be used to generate a magnetic fieldor to deliver ablation energy.

While the ablation catheter of FIGS. 4 and 4 a is shown with an umbrellatip geometry, it should be appreciated that numerous configurations ofcarrier arms, such as spiral, zigzag, and other patterns could beemployed. These carrier assemblies are configured to provide sufficientforces to maximally engage the appropriate ablation element with thetissue to be ablated, without adversely impacting neighboring structuresand other tissues. While the carrier assembly 120 of FIG. 4 “folds in”during retraction of shaft 150, other collapsing configurations can beemployed such as the “fold out” configuration of the catheter of FIG. 2a, or configuration in which the carrier assembly transforms from aspiral, zigzag, or other curvilinear shape to a relatively straight orlinear configuration as it is retracted and captured by the lumen ofcatheter shaft 101. Electrodes 130 of carrier assembly of FIG. 4 areshown facing out from the distal end of shaft 101 such that advancementor “pushing” of carrier assembly 120 engages electrodes 130 with tissue.In an alternative embodiment, electrodes are positioned, alternativelyor additionally, to face toward the distal end of shaft 101. Theseelectrodes may be mounted to proximal arm segment 125 such thatretraction or “pulling” of carrier assembly 120, once deployed, engagesthese rear facing electrodes with tissue.

Ablation catheter 100 and RF delivery unit 200 are configured to ablatetissue with minimal power and precise control. RF Power levels arepreferably less than 10 watts per electrode, and preferably 3 to 5watts. Electrodes 130 are powered to reach an ablation temperature ofapproximately 60° C. The electrode geometries of the present invention,described in detail in reference to FIGS. 5 a through 5 f and FIGS. 6 athrough 6 c, provide numerous and varied benefits including enhancedcooling properties. Electrodes of the present invention are configuredto transition from an ablation temperature of 60° C. to body temperatureof 37° C. in less than 20 seconds and preferably less than ten seconds.These electrodes are further configured to increase from bodytemperature to ablation temperature in less than 5 seconds. In apreferred embodiment, bipolar RF energy is delivered subsequent tomonopolar delivery. The electrodes and power delivery subsystems of thepresent invention are configured to allow the electrode and neighboringtissue to decrease in temperature during the bipolar RF energy deliveryfollowing the monopolar delivery. This bimodal, sequential powerdelivery reduces procedure time, allows precise control of lesion depthand width, and reduces large swings in ablation temperatures. In anotherpreferred embodiment, the temperature in the tissue in proximity to theelectrode actually continues to increase as the electrode temperaturedecreases, such as during the bipolar delivery following monopolardelivery. In an alternative embodiment, the monopolar delivery cycle,the bipolar delivery cycle, or both, are followed by a period of time inwhich no RF energy is delivered. During this “off” time period, noenergy may be delivered or an alternative energy may be delivered suchas cryogenic energy that actually decreases the temperature of thetissue in order to ablate.

In a preferred embodiment, parameters associated with the bipolar andmonopolar energy delivery are adjusted during the procedure,automatically by the system and/or manually by the operator. The energydelivery parameters are adjusted by measured, calculated or otherwisedetermined values include those relating to: energy deliveredmeasurements such as voltage or current delivered to an electrode; forceor pressure measurement such as the force exerted by the carrierassembly as measured by an integral strain gauge; other ablationcatheter or ablation system parameter; temperature of tissue; rate ofchange of temperature of tissue; temperature of an electrode or otherablation element; rate of change of temperature of an electrode or otherablation element; EKG; tissue thickness; tissue location; cardiacflow-rate; other patient physiologic and other patient parameters; andcombinations thereof. The energy delivery drive parameters may beadjusted by a combination of these determined values. In order toautomatically modify an energy delivery parameter, or to notify anoperator of a condition, these determined values are compared to athreshold, such as via a threshold comparator integral to the interfaceunit of the present invention. Threshold values can be calculated by thesystem or can be entered by the operator into a user interface of thesystem.

Energy delivered measurements, such as current, voltage and powermeasurements, which may be compared to a threshold value, includeaverage energy; instantaneous energy; peak energy; cumulative orintegrated energy amounts; and combinations thereof. In the catheter andsystem of the present invention, average power is approximately 5 Wattsand less, cumulative energy for a cycle of bipolar and monopolardelivery is typically less than 500 Watt-seconds and preferably lessthan 300 Watt-seconds (5 watts for 60 seconds). Each threshold value maychange over time and may be adjustable by an operator such as via apassword enabled user interface. Cumulative determined values, such ascumulative energy delivered and “time at temperature” values may be ableto be reset, such as automatically by the system and/or manually by anoperator. Automatic resets may occur at specific events such as eachtime an ablation element is repositioned on tissue or each time energydelivered changes states, including the switching of electrodesreceiving energy or the completion of a monopolar-bipolar deliverycycle.

Determined values such as temperature measurements may be made fromsingle or multiple sensors, such as multiple temperature sensors duringa single ablation cycle. In a preferred embodiment, multiple sensors areused and the more extreme (e.g. a higher temperature) value is comparedto a threshold. When the threshold comparator determines a particularthreshold has been reached, the system can adjust or otherwise react invarious ways. In a preferred embodiment, the system enters an alarm oralert state. In another preferred embodiment, the energy deliverytransmitted to an ablation element is modified; such as to cease orreduce the amount of RF energy delivered to an electrode. Numerousenergy delivery parameters can be modified including but not limited to:current level; voltage level; frequency (usually fixed at 500 KHz);bipolar delivery “on” times; monopolar delivery “on” times; no energydelivery “on” times; electrode selected such as bipolar return electrodeselected; and combinations thereof.

The automatic and manual adjustments of the present invention aretriggered by comparing a measured, calculated or otherwise determinedvalue to a threshold. These adjustments improve numerous outcomes of theproposed ablation therapy including those associated with improvedefficacy and reduced adverse events. Specific benefits include precisioncontrolled depth and width of lesions through a combination of bipolarand monopolar sequential duty cycles. The system is adjustable by theoperator to modify intended lesion geometry to safely avoid structureslike pulmonary vein lumens and the esophagus, as well as work inportions of the atrial wall that require deep lesions to effectivelyinterrupt aberrant pathways.

Referring now to FIGS. 5 a through 5 f, multiple preferred embodimentsof electrode-type ablation element of the present invention areillustrated. These electrodes are shown in sectional view in contactwith tissue 30 just prior to or during delivery of energy to tissue 30via the electrode. Each of the electrodes of FIGS. 5 a through 5 f areintended to maximize cooling, minimize energy delivered to non-targetedtissue (e.g. blood), or both. Certain electrodes are configured tominimize “low flow” areas for blood, such blood more likely to absorbenough energy to clot during an energy delivery cycle. The electrodecross sections assume various geometries such as triangular,semi-circular and crescent shaped, and are all preferably relativelyuniform along their length such as to simplify their manufacturing.Cross sectional geometries are configured to create lesions of specificwidths and depths, and to otherwise minimize trauma to neighboringtissue such as when force is applied to press the electrode “into” thetissue to be ablated. In a preferred embodiment, each of the electrodesof FIGS. 5 a through 5 f includes one or more temperature sensors, suchas a thermocouple in a non-energy delivery portion.

Referring specifically to FIG. 5 a, electrode 130 b is displayedincluding a triangular cross section and configured to be placed by anoperator with base 136 in contact with tissue 30. Electrode 130 bincludes an isosceles triangle cross section, with two equal sides,sides 137 and 138, each positioned in circulating blood when ablationenergy, such as RF energy, is being delivered via wires 134 and 135.Electrode 130 b is fixedly mounted to distal arm segment 127, as hasbeen described in detail in reference to previous figures. Distal armsegment 127 is sufficiently rigid to allow the operator to apply a forceto electrode 130 b such that electrode 130 b can be pressed, as shown,into tissue 30. The transition point from base 136 to side 137 and frombase 136 to side 138 each are rounded such that although electrode 130 bis slightly depressed into tissue 30, low blood flow area 31 (an areawhere blood will tend to heat up at a faster rate) is minimized as wellas tension in the neighboring tissue. The surface area of sides 137 and138 are sufficiently large (i.e. the combined lengths of sides 137 and138 is sufficiently long) such that their combined surface area isgreater than 60% of the overall total surface area of electrode 130 b,preferably greater than 75% of the total. This high percentage ofsurface area in the circulating blood provides rapid and efficientcooling of electrode 130 b.

Referring specifically to FIG. 5 b, electrode 130 c is displayedincluding a triangular cross section and configured to be placed by anoperator with the majority of sides 137 and 138 in contact with tissue30. Electrode 130 c includes an isosceles triangle cross section andbase 136 positioned in circulating blood when ablation energy, such asRF energy, is being delivered via wires 134 and 135. Electrode 130 c isfixedly mounted to distal arm segment 127, as has been described indetail in reference to previous figures. Distal arm segment 127 issufficiently rigid to allow the operator to apply a force to electrode130 c such that electrode 130 c can be pressed, as shown, into tissue30. The surface area of sides 137 and 138 are sufficiently large suchthat their combined surface area is greater than 60% of the overalltotal surface area of electrode 130 c, preferably greater than 70% ofthe total. This high percentage of surface area in contact with tissueminimizes the amount of energy delivered by electrode 130 c into theneighboring blood. The energy delivery parameters are chosen such as toprevent the blood residing in or near low flow area 31 from clotting.

Referring specifically to FIG. 5 c, electrode 130 d is displayedincluding a laminate construction with a triangular cross section andconfigured to be placed by an operator with the majority of sides 137and 138 in contact with tissue 30. Electrode 130 d is configured to bothimprove cooling, and maximize energy delivered to tissue versus blood.Electrode 130 d includes an isosceles triangle cross section, with base136 positioned in circulating blood when ablation energy, such as RFenergy, is being delivered via wires 134 and 135. Electrode 130 d isfixedly mounted to distal arm segment 127, as has been described indetail in reference to previous figures. Distal arm segment 127 issufficiently rigid to allow the operator to apply a force to electrode130 d such that electrode 130 d can be pressed, as shown, into tissue30. Electrode 130 d has a laminate construction that includes a firstportion that receives and delivers energy to tissue, electrical portion132, a segment preferably constructed of standard RF electrode materialsdescribed hereabove. Electrical portion 132 makes up the majority ofsides 137 and 138 and is sized such that all or nearly all of itssurface area is in contact with tissue 30 during delivery of energy.Electrode 130 d has a second portion that is thermally conductive,thermal portion 139. Thermal portion 139 is either electricallynon-conductive, minimally electrically conductive, and/or electricallyisolated from electrical portion 132 such that thermal portion 139 doesnot deliver energy when energy is applied to and delivered by electricalportion 132. Thermal portion 139 may be constructed of standardelectrode materials but be electrically isolated from electrical portion132 such as with insulating glue 146. In this configuration and in anadditional embodiment, thermal portion 139 may also (in addition toelectrical portion 132) independently be used to map or deliver energywith different drive wires not shown. Alternatively, thermal portion 139may be a plastic with high thermal conductivity such as a Konduit™thermally conductive thermoplastic compound manufactured by LNPEngineering Plastics of Exton, Pa. Thermal portion 139 makes up a smallportion of each of side 137 and side 138, and the entirety of base 136such that when electrode 130 d is positioned “into” tissue by theoperator, most of thermal portion 139 is in the circulating blood,dissipating heat from electrical portion 132 and the neighboring tissue.Thermal portion 139 is sized such that no significant energy isdelivered to low flow area 31, greatly reducing any chance of clotformation. Electrode 130 d is configured to apply the great majority ofthe energy it receives into tissue and not blood, as well as provideenhanced cooling by having a thermal portion with significant surfacearea and/or efficient thermal mass that resides in the circulating bloodduring energy delivery. In an alternative embodiment, thermal portion139 further includes a projecting fin to increase the transfer of heatfrom electrode 130 d into the blood stream as has been described inreference to FIG. 2 b hereabove. In an alternative embodiment, notshown, electrode 130 d is fixedly attached to distal arm segment 127 inthe opposite (mirrored) orientation such that base 136 is in contactwith tissue 30 during ablation, similar to the attachment configurationof electrode 130 b of FIG. 5 a. In this particular preferred embodiment,electrical portion 132 makes up the majority of base 136, and thermalportion 139 makes up both sides 137 and 138 as well as two small endportions of base 136, such that all of the energy delivered from base136 is transferred to tissue 30, and a greatly increased surface areacomprising sides 137 and 138 is in contact with circulating blood tocool electrode 130 d.

Referring specifically to FIG. 5 d, electrode 130 e is displayedincluding a similar construction to electrode 130 d of FIG. 5 c with asemi-circular cross section instead of a triangular cross section and aportion which does not deliver energy but acts as a heat sink. Thecrescent shaped cross section of electrode 130 e causes less tissuedeflection per unit force than the triangular cross section of electrode130 d of FIG. 5 c, and may be preferable for ablating a wider lesion,ablating in areas of thin or weakened tissue, or for other operatorpreferences or patient requirements. Electrode 130 e is configured to beplaced by an operator with a central portion of rounded side 137 incontact with tissue 30. Electrode 130 e is configured to both improvecooling, and maximize energy delivered to tissue versus blood. Base 136is positioned in circulating blood when ablation energy, such as RFenergy, is being delivered via wires 134 and 135. Electrode 130 e isfixedly mounted to distal arm segment 127, as has been described indetail in reference to previous figures. Distal arm segment 127 issufficiently rigid to allow the operator to apply a force to electrode130 e such that electrode 130 e can be pressed, as shown, into tissue30. Electrode 130 e has a laminate construction that includes a firstportion that receives and delivers energy to tissue, electrical portion132, a segment preferably constructed of standard RF electrode materialsdescribed hereabove. Electrical portion 132 is sized such that all ornearly all of its surface area is in contact with tissue 30 duringdelivery of energy. Electrode 130 e has a second portion that isthermally conductive, thermal portion 139. Thermal portion 139 is eitherelectrically non-conductive or electrically isolated from electricalportion 132 such that thermal portion 139 does not deliver energy whenenergy is applied to and delivered by electrical portion 132. Thermalportion 139 is a plastic with high thermal conductivity such as aKonduit™ thermally conductive thermoplastic compound manufactured by LNPEngineering Plastics of Exton, Pa. and is attached to electrical portion132 at joint 147. Alternatively, thermal portion 139 may be constructedof standard electrode materials and be electrically isolated fromelectrical portion 132 such as with insulating glue, not shown. Thermalportion 139 is appropriately sized such that when the operator positionselectrode 130 d into tissue, most of thermal portion 139 is in thecirculating blood, efficiently dissipating heat from electrical portion132 and the neighboring tissue. Thermal portion 139 is sized such thatno significant energy is delivered to low flow area 31, greatly reducingany chance of clot formation. Electrode 130 e is configured to apply thegreat majority of the energy it receives into tissue and not blood, aswell as provide enhanced cooling by having a thermal portion withsignificant surface area and/or efficient thermal mass that resides inthe circulating blood during energy delivery. In an alternativeembodiment, thermal portion 139 further includes a fin to increase thetransfer of heat from electrode 130 e into the blood stream.

Referring specifically to FIG. 5 e, electrode 130 f is displayedincluding a crescent shaped cross section and configured to be placed byan operator with side 137 in contact with tissue 30. The crescent shapedcross section of electrode 130 f causes less tissue deflection per unitforce than the triangular cross section of electrode 130 d of FIG. 5 c,and may be preferable for ablating a wider lesion, ablating in areas ofthin or weakened tissue, or for other operator preferences or patientrequirements. The surface area of base 136, positioned in circulatingblood when ablation energy is being delivered via wires 134 and 135, isless that the surface area of side 137, which causes the majority ofenergy delivered to electrode 130 f to be delivered to tissue versusblood. The crescent shape of electrode 130 f is chosen to minimizetrauma as electrode 130 f is being pressed into the tissue. Electrode130 f is fixedly mounted to distal arm segment 127, as has beendescribed in detail in reference to previous figures. Distal arm segment127 is sufficiently rigid to allow the operator to apply a force toelectrode 130 f such that electrode 130 f can be pressed, as shown, intotissue 30. The crescent shape greatly reduces the volume of low flowarea 31, minimizing the chance of blood clotting.

Referring specifically to FIG. 5 f, electrode 130 g is displayedincluding a crescent shaped cross section and configured to be placed byan operator with side 137 in contact with tissue 30. The crescent shapedcross section of electrode 130 g causes less tissue deflection per unitforce than the triangular cross section of electrode 130 d of FIG. 5 c,and may be preferable for ablating a wider lesion, ablating in areas ofthin or weakened tissue, or for other operator preferences or patientrequirements. As compared to electrode 130 f of FIG. 5 e, side 137 has aserpentine segment that greatly increases the surface area of side 137.In should be appreciated that numerous other configurations can be usedto increase the length of side 137 and the resultant surface area, suchas zigzag segments and combinations of straight and non-straight linesegments. The surface area of base 136, positioned in circulating bloodwhen ablation energy is being delivered via wires 134 and 135, is muchless that the surface area of side 137, which causes a great majority ofenergy delivered to electrode 130 g to be delivered to tissue versusblood. The crescent shape of electrode 130 g is chosen to minimizetrauma as electrode 130 f is being pressed into the tissue. Electrode130 g is fixedly mounted to distal arm segment 127, as has beendescribed in detail in reference to previous figures. Distal arm segment127 is sufficiently rigid to allow the operator to apply a force toelectrode 130 g such that electrode 130 g can be pressed, as shown, intotissue 30. The crescent shape greatly reduces the volume of low flowarea 31, minimizing the chance of blood clotting. In an alternativeembodiment, electrode 130 g is fixedly mounted to distal arm segment 127in the opposite (mirrored) orientation such that the large surface areaserpentine side 137 is in the circulating blood during ablation,providing a highly efficient cooling electrode configuration.

Referring now to FIGS. 6 a through 6 cf, multiple preferred embodimentsof electrode-type ablation element of the present invention areillustrated. Each of the electrodes of FIGS. 6 a through 6 c areintended to maximize cooling, minimize energy delivered to non-targetedtissue (e.g. blood), or both. Certain electrodes are configured tominimize “low flow” areas for blood, such blood more likely to absorbenough energy to clot during an energy delivery cycle. The electrodescross sections assume various geometries and are all preferablyrelatively uniform along their length such as to simplify theirmanufacturing. Cross sectional geometries are configured to createlesions of specific widths and depths, and to otherwise minimize traumato neighboring tissue such as when force is applied to press theelectrode “into” the tissue to be ablated. In a preferred embodiment,each of the electrodes of FIGS. 6 a through 6 c includes one or moretemperature sensors, such as a thermocouple in a non-energy deliveryportion.

Referring specifically to FIG. 6 a, electrode 130 h, displayed in asectional view, has a triangular cross section and is configured to beplaced by an operator with base 136 in contact with tissue to beablated. Electrode 130 h includes an isosceles triangle cross section,with two equal sides, sides 137 and 138, each positioned in circulatingblood when ablation energy, such as RF energy, is being delivered viawires 134 and 135. Electrode 130 h is fixedly mounted to distal armsegment 127, as has been described in detail in reference to previousfigures. Distal arm segment 127 is sufficiently rigid to allow theoperator to apply a force to electrode 130 h such that electrode 130 hcan be pressed into the tissue to be ablated. The transition point frombase 136 to side 137 and from base 136 to side 138 each are rounded toreduce tissue trauma and low blood flow areas during ablation. Thethickness of sides 137 and 138 as well as base 136 are chosen to havesufficient mass to effectively deliver energy to tissue withoutoverheating, while minimizing a large thermal mass that would bedifficult to cool. In a preferred embodiment, sides 137 and 138 have asmaller wall thickness than base 136, differentiation in thickness notillustrated. Side 137 and side 138 are not connected, leaving opening148 opposite side 136, to provide enhanced cooling such as by increasingthe effective surface area (allowing circulating blood to pass by theinterior surfaces of sides 137 and 138 and potentially base 136). Thesurface area of sides 137 and 138 are sufficiently large (i.e. thecombined lengths of sides 137 and 138 is sufficiently long) such thattheir combined surface area is greater than 60% of the overall totalsurface area of electrode 130 h, preferably greater than 75% of thetotal. In alternative embodiments, side 137 and/or side 138 comprises anon-straight segment such as a curved segment, serpentine segment,zigzag segment, or combinations of straight and non-straight segments.The high percentage of surface area in the circulating blood, inaddition to the advantages provided by opening 148, provide rapid andefficient cooling of electrode 130 h.

Referring specifically to FIG. 6 b, electrode 130 i, displayed in asectional view, has a triangular cross section and is configured to beplaced by an operator with base 136 in contact with tissue to beablated. Electrode 130 i includes an isosceles triangle cross section,with two equal sides, sides 137 and 138, each positioned in circulatingblood when ablation energy, such as RF energy, is being delivered viawires 134 and 135. Electrode 130 i is fixedly mounted to distal armsegment 127, as has been described in detail in reference to previousfigures. Distal arm segment 127 is sufficiently rigid to allow theoperator to apply a force to electrode 130 i such that electrode 130 ican be pressed into the tissue to be ablated. The transition point frombase 136 to side 137 and from base 136 to side 138 each are rounded toreduce tissue trauma and low blood flow areas during ablation. Thethickness of sides 137 and 138 as well as base 136 are chosen to havesufficient mass to effectively deliver energy to tissue withoutoverheating, while minimizing a large thermal mass that would bedifficult to cool. In a preferred embodiment, sides 137 and 138 have asmaller wall thickness than base 136, differentiation in thickness notillustrated. Side 137 and side 138 are not connected, leaving opening148 opposite side 136, to provide enhanced cooling such as by increasingthe effective surface area (allowing circulating blood to pass by theinterior surfaces of sides 137 and 138 and potentially base 136).Included on each of side 137 and side 138 is a projecting fin, fin 133 aand 133 b respectively, which increase the surface areas of sides 137and 138. The surface areas of sides 137 and 138 are sufficiently large(i.e. the combined lengths of sides 137 and 138 is sufficiently long)such that their combined surface area is greater than 60% of the overalltotal surface area of electrode 130 i, preferably greater than 75% ofthe total. The high percentage of surface area in the circulating bloodprovides rapid and efficient cooling of electrode 130 i.

Referring specifically to FIG. 6 c, electrode 130 j, displayed in a sideview, is configured to be placed by an operator with base 136 in contactwith tissue to be ablated. Electrode 130 j includes a rectangularcross-section, not illustrated, with four projecting fins 133 a, 133 b,133 c and 133 d extending from a top surface 149. Top surface 149 andeach projecting fin are each positioned in circulating blood whenablation energy, such as RF energy, is being delivered via wires 134 and135. Electrode 130 j is fixedly mounted to distal arm segment 127, ashas been described in detail in reference to previous figures. Distalarm segment 127 is sufficiently rigid to allow the operator to apply aforce to electrode 130 j such that electrode 130 j can be pressed intothe tissue to be ablated. The thickness of base 136, top surface 149 andprojections 133 a, 133 b, 133 c and 133 d are chosen to have sufficientmass to effectively deliver energy to tissue without overheating, whileminimizing a large thermal mass that would be difficult to cool. In apreferred embodiment, top surface 149 and fins 133 a, 133 b, 133 c, and133 d have a smaller wall thickness than base 136, differentiation inthickness not illustrated. The surface areas of top surface 149 and fins133 a, 133 b, 133 c and 133 d are sufficiently large such that theircombined surface area is typically greater than 60% of the overall totalsurface area of electrode 130 i, preferably greater than 85% of thetotal. The high percentage of surface area in the circulating bloodprovides rapid and efficient cooling of electrode 130 j.

It should be understood that numerous other configurations of thesystems, devices and methods described herein may be employed withoutdeparting from the spirit or scope of this application. The ablationcatheter includes one or more ablation elements such as the electrodesdescribed in reference to FIGS. 5 a through 5 f and FIGS. 6 a through 6c. These electrodes include various cross-sectional geometries,projecting fins, energy delivering portions and non-energy deliveringportions, and other features described in reference to these drawings.It should be appreciated that one or more features described inreference to one specific electrode can be combined with one or morefeatures described in reference to a different electrode, in whole or inpart, in any combination, without departing from the spirit and scope ofthis application. The electrodes can be configured to maximize tissuecontact of the energy delivering portion(s), maximize cooling, or both.Clinician preferences, broad patient population requirements, and othertreatment goals are likely to require catheters with differentperformance parameters, as are described in detail throughout thisapplication, to both safely and effectively block an aberrant conductivepathway. The systems, catheters and ablation elements of the presentinvention are designed to achieve specific depths and widths of lesions,while preventing overheating that may damage more tissue than necessaryand/or create dangerous embolus such as blood clots or fragmentedtissue. The systems of the present invention are configured toautomatically, semi-automatically or manually adjust the energy appliedto the ablation elements such as by adjusting one or more of thefollowing: the level or amount of energy delivered; type of energydelivered; drive signal supplied such as monopolar and bipolar; phasing,timing or other time derived parameter of the applied energy; andcombinations thereof.

The ablation elements of the present invention are attached to energydelivery conduits that carry the energy to the electrode that issupplied by the interface unit. RF electrodes are connected to wires,preferably in a configuration with individual wires to at least twoelectrodes to allow independent drive of the electrodes includingsequential and simultaneous delivery of energy from multiple electrodes.Alternative or additional energy delivery conduits may be employed, suchas fiber optic cables for carrying light energy such as laser energy;tubes that carry cryogenic fluid for cryogenic ablation or saline forsaline mediated electrical energy ablation; conduits for carrying soundenergy; other energy delivery conduits; and combinations thereof.

The system includes multiple functional components, such as the ablationcatheter, and the interface unit. The interface unit preferably energysupply means and a user interface, as well as calculating means forinterpreting data such as mapping data and data received from one ormore sensors, as well as means of comparing measured, calculated orotherwise determined values to one or more thresholds. In a preferredembodiment, a low level energy delivery is performed prior to a higherlevel energy delivery. During or after the low energy delivery, one ormore parameters are measured, calculated or otherwise determined thatare used to determine a threshold for the second energy delivery, suchas a second delivery of energy to the same relative tissue location.

The interface unit further includes means of adjusting one or moresystem parameters, such as the amount type, or configuration of energybeing delivered, when a particular threshold is met. The ablationcatheter includes at least one ablation element for delivering energy totissue such as cardiac tissue. Cardiac tissue applicable for ablationincludes left and right atrial walls, as well as other tissues includingthe septum and ventricular tissue. The ablation catheter of the presentinvention includes a flexible shaft with a proximal end, a distal end,and a deployable carrier assembly with at least one, and preferablymultiple ablation elements. The flexible shafts may include one or morelumens, such as thru lumens or blind lumens. A thru lumen may beconfigured to allow over-the-wire delivery of the catheter or probe.Alternatively the catheter may include a rapid exchange sidecar at ornear its distal end, consisting of a small projection with a guidewirelumen therethrough. A lumen may be used to slidingly receive a controlshaft with a carrier assembly on its distal end, the carrier assemblydeployable to exit either the distal end or a side hole of the flexibleshaft. The advancement of the carrier assembly, such as through a sidehole, via controls on the proximal end of the device, allows specificdisplacement of any functional elements, such as electrodes, mounted onthe carrier assembly. Other shafts may be incorporated which act as arotational linkage as well as shafts that retract, advance or rotate oneor more components. A lumen may be used as an inflation lumen, whichpermits a balloon mounted on a portion of the exterior wall of theflexible shaft to be controllably inflated and deflated. The balloon maybe concentric or eccentric with the central axis of the shaft, it may bea perfusion balloon, and may include an in-line pressure sensor to avoidover-pressurizing. A lumen may be used to receive a rotating linkage,such as a linkage used to provide high-speed rotation of an array ofultrasound transducers mounted near the distal end of the linkage. Eachdevice included in a lumen of the flexible shafts may be removable orconfigured to prevent removal.

The ablation catheter of the present invention may include one or morefunctional elements, such as one or more location elements, sensors,transducers, antennas, or other functional components. Functionalelements can be used to deliver energy such as electrodes deliveringenergy for tissue ablation, cardiac pacing or cardiac defibrillation.Functional elements can be used to sense a parameter such as tissuetemperature; cardiac signals or other physiologic parameters; contactwith a surface such as the esophageal or atrial walls of a patient; anenergy parameter transmitted from another functional element such asamplitude, frequency; phase; direction; or wavelength parameters; andother parameters. In a preferred embodiment of the present invention,the ablation catheter includes multiple functional elements. In anotherpreferred embodiment, the ablation catheter includes a deflectabledistal end; such as a deflected end that causes one or more functionalelements to make contact with tissue. Deflection means may include oneor more of: a pull wire; an expandable cage such as an eccentric cage;an expandable balloon such as an eccentric balloon; an expandable cuff;a deflecting arm such as an arm which exits the flexible catheter shaftin a lateral direction; and a suction port.

The ablation catheter of the present invention preferably includes ahandle on their proximal end. The handle may be attached to an outersheath, allowing one or more inner shafts or tubes to be controlled withcontrols integral to the handle such as sliding and rotating knobs thatare operable attached to those shafts or tubes. Alternatively, thehandle may be attached to a shaft that is slidingly received by an outersheath, such that an operator can advance and retract the shaft byadvancing and retracting the handle and holding the sheath in arelatively fixed position. The handle may include one or more attachmentports, such as attachment ports which electrically connect to one ormore wires; ports which provide connection to optical fibers providinglaser or other light energies; ports which fluidly connect to one ormore conduits such as an endoflator for expanding a balloon with salineor a source of cooling fluids; and combinations thereof. Other controlsmay be integrated into the handle such as deflecting tip controls,buttons that complete a circuit or otherwise initiate an event such asthe start of energy delivery to an ablation element. In addition, thehandle may include other functional components including but not limitedto: transducers such as a sound transducer which is activated to alertan operator of a change is status; a visual alert component such as anLED, a power supply such as a battery; a lock which prevents inadvertentactivation of an event such as energy delivery; input and output devicesthat send and receive signals from the interface unit of the presentinvention; and combinations thereof.

The interface unit of the present invention provides energy to theablation elements of the ablation catheter. In preferred embodiments,one or more ablation elements are electrodes configured to deliver RFenergy. Other forms of energy, alternative or in addition to RF, may bedelivered, including but not limited to: acoustic energy and ultrasoundenergy; electromagnetic energy such as electrical, magnetic, microwaveand radiofrequency energies; thermal energy such as heat and cryogenicenergies; chemical energy; light energy such as infrared and visiblelight energies; mechanical energy; radiation; and combinations thereof.The ablation elements can deliver energy individually, in combinationwith or in serial fashion with other ablation elements. The ablationelements can be electrically connected in parallel, in series,individually, or combinations thereof. The ablation catheter may includecooling means to prevent undesired tissue damage and/or blood clotting.The ablation elements may be constructed of various materials, such asplates of metal and coils of wire for RF or other electromagnetic energydelivery. The electrodes can take on various shapes including shapesused to focus energy such as a horn shape to focus sound energy, andshapes to assist in cooling such as a geometry providing large surfacearea. Electrodes can vary within a single carrier assembly, such as aspiral array of electrodes or an umbrella tip configuration whereinelectrodes farthest from the central axis of the catheter have thelargest major axis. Wires and other flexible energy delivery conduitsare attached to the ablation elements, such as electrical energycarrying wires for RF electrodes or ultrasound crystals, fiber opticcables for transmission of light energy, and tubes for cryogenic fluiddelivery.

The ablation elements requiring electrical energy to ablate requirewired connections to an electrical energy power source such as an RFpower source. In configurations with large numbers of electrodes,individual pairs of wires for each electrode may be bulky and compromisethe cross-sectional profile of the ablation catheter. In an alternativeembodiment, one or more electrodes are connected in serial fashion suchthat a reduced number of wires, such as two wires, can be attached totwo or more electrodes and switching or multiplexing circuitry areincluded to individually connect one or more electrodes to the ablativeenergy source. Switching means may be a thermal switch, such that as afirst electrodes heats up, a single pole double throw switch changestate disconnecting power from that electrode and attaching power to thenext electrode in the serial connection. This integral temperatureswitch may have a first temperature to disconnect the electrode, and asecond temperature to reconnect the electrode wherein the secondtemperature is lower than the first temperature, such as a secondtemperature below body temperature. In an alternative embodiment, eachelectrode is constructed of materials in their conductive path such thatas when the temperature increased and reached a predetermined threshold,the resistance abruptly decreased to near zero, such that powerdissipation, or heat, generated by the electrode was also near zero, andmore power could be delivered to the next electrode incorporating theabove switching means

The interface unit of the present invention includes a user interfaceincluding components including but not limited to: an ultrasound monitorsuch as an ultrasound monitor in communication with one or moreultrasound crystals near a temperature sensor of an esophageal probe orultrasound crystals within an electrode carrier assembly of the ablationcatheter; an x-ray monitor such as a fluoroscope monitor used to measurethe distance between two or more location elements; other user outputcomponents such as lights and audio transducers; input components suchas touch screens, buttons and knobs; and combinations thereof. In apreferred embodiment, the interface unit provides functions in additionto providing the energy to the ablation catheter including but notlimited to: providing a cardiac mapping function; providing cardiacdefibrillation energy and control; providing cardiac pacing energy andcontrol; providing a system diagnostic such as a diagnostic confirmingproper device connection; providing the calculating function of thepresent invention; providing a signal processing function such asinterpreting signals received from one or more sensors of a probe, suchas an esophageal probe, and/or the ablation catheter; providing drivesignals and/or energy to one or more functional elements of the ablationcatheter; providing a second energy type to the ablation elements of theablation catheter; and combinations thereof.

In a preferred embodiment, the interface unit provides an analysisfunction to determine one or more system parameters that correlate toablation settings, the parameters including but not limited to: anenergy delivery amount; an energy delivery frequency; an energy deliveryvoltage; an energy delivery current; an *energy delivery temperature; anenergy delivery rate; an energy delivery duration; an energy deliverymodulation parameter; an energy threshold; another energy deliveryparameter; a temperature threshold; an alarm threshold; another alarmparameter; and combinations thereof. The analysis function compares ameasured, calculated or otherwise determined function to a thresholdvalue, such as a threshold value settable by an operator of the system.In a preferred embodiment, the interface unit receives temperatureinformation from multiple sensors of the ablation catheter and/or otherbody inserted devices, and the highest reading received is compared to atemperature threshold such as a temperature threshold determined by thelocation of tissue being ablated. The analysis function includes one ormore algorithms that mathematically process information such as signalsreceived from sensors of the ablation catheter or other device;information entered into the user interface of the interface unit by theoperator; embedded electronic information uploaded from the ablationcatheter or other device such as information determined during themanufacture of the catheter or device; and combinations thereof. In apreferred embodiment, the ablation setting determined by the analysisfunction is provided to the operator via a display or other userinterface output component.

The interface unit of the present invention performs one or moremathematical functions, signal processing functions; signal transmissionfunctions; and combinations thereof, to determine a system performance(e.g. during ablation) or other system parameter. A calculation mayinclude a function performed by an operator of the system such as adistance value that is entered into the interface unit after ameasurement is performed such as a measurement made from an IVUS monitoror a fluoroscopy screen. In a preferred embodiment, energy delivered,such as a maximum cumulative energy, maximum peak energy or maximumaverage energy is limited by a threshold. In a preferred embodiment,when a temperature reaches a threshold, one or more system parametersare modified. These modifications include but are not limited to: athreshold parameter such as an increased temperature threshold; an alarmor alert parameter such as an audible alarm “on” state; an energyparameter such as a parameter changing energy type or modifying energydelivery such as switching from RF energy to cryogenic energy orstopping energy delivery; a sensor parameter such as a parameter whichactivates one or more additional sensors; cooling apparatus parametersuch as a parameter activating a cooling apparatus; a parameter thatchanges the polarity of energy delivery or the modulation of energydelivery such as a parameter that switches from monopolar to bipolardelivery or phased monopolar-bipolar to bipolar; and combinationsthereof.

The system of the present invention preferably includes multiplefunctional elements integral to the ablation catheter and/or othersystem component. These functional elements may be mounted on the outerwall of the flexible shaft of the device. Alternatively or additionally,one or more functional elements may be mounted to a balloon, such as aperfusion balloon, eccentric balloon or concentric balloon and/orelements may be mounted to a carrier assembly such as a carrier assemblythan exits the distal end or a side hole of the flexible shaft. Thesefunctional elements may be covered with a membrane and multiple elementsmay be configured in an array such as an array that is rotated within alumen of the flexible shaft. Functional elements may be placed on thepatient's chest, such as EKG electrodes, pacing electrodes ordefibrillation electrodes. Functional elements include but are notlimited to: sensors such as temperature sensors; transmitters such asenergy transmitting electrodes, antennas and electromagnetictransmitters; imaging transducers; signal transmitters such as drivesignal transmitters.

Functional elements may include sensing functions such a sensor todetect a physiologic parameter. In a preferred embodiment, one or morefunctional elements are configured as sensors to receive signals thatare indicative of one or more cardiac functions of the patient. Sensorsmay include but are not limited to: an electrical signal sensor such asa cardiac electrode; a temperature sensor such as a thermocouple; animaging transducer such as an array of ultrasound crystals; a pressuresensor; a pH sensor; a blood sensor, a respiratory sensor; an EEGsensor, a pulse oximetry sensor; a blood glucose sensor; an impedancesensor; a contact sensor; a strain gauge; an acoustic sensor such as amicrophone; a photodetector such as an infrared photodetector; andcombinations thereof. Functional elements alternatively or additionallyinclude one or more transducers. The transducer may be a locationelement; a transmitter such as a transmitting antenna, an RF electrode,a sound transmitter; a photodiode, a pacing electrode, a defibrillationelectrode, a visible or infrared light emitting diode and a laser diode;a visualization transducer such as an ultrasound crystal; andcombinations thereof.

Numerous kit configurations are also to be considered within the scopeof this application. An ablation catheter is provided with multiplecarrier assemblies. These carrier assemblies can be removed for thetubular body member of the catheter, or may include multiple tubularbody members in the kit. The multiple carrier assemblies can havedifferent patterns, different types or amounts of electrodes, and havenumerous other configurations including compatibility with differentforms of energy. Multiple sensors, such as EKG skin electrodes may beincluded, such as electrodes that attach to the interface unit of thepresent invention. A kit may include one or more catheters, such as anultrasound catheter, which are configured to enter and extend distallyin a lumen of the ablation catheter. One or more esophageal probes maybe included such as probes with different tip or sensor configurations.

Though the ablation device has been described in terms of its preferredendocardial and percutaneous method of use, the array may be used on theheart during open-heart surgery, open-chest surgery, or minimallyinvasive thoracic surgery. Thus, during open-chest surgery, a shortcatheter or cannula carrying the carrier assembly and its electrodes maybe inserted into the heart, such as through the left atrial appendage oran incision in the atrium wall, to apply the electrodes to the tissue tobe ablated. Also, the carrier assembly and its electrodes may be appliedto the epicardial surface of the atrium or other areas of the heart todetect and/or ablate arrhythmogenic foci from outside the heart.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims. In addition,where this application has listed the steps of a method or procedure ina specific order, it may be possible, or even expedient in certaincircumstances, to change the order in which some steps are performed,and it is intended that the particular steps of the method or procedureclaim set forth herebelow not be construed as being order-specificunless such order specificity is expressly stated in the claim.

1-71. (canceled)
 72. An ablation system for an operator to treat apatient, said system comprising: an ablation catheter including at leastone ablation element for delivering energy to tissue, said cathetercomprising a flexible shaft with a proximal end and a distal end; and;an interface unit for providing energy to the ablation catheter; whereinthe interface unit monitors at least one parameter of the system toprevent energy delivered from exceeding a threshold value, saidthreshold value determined by the at least one ablation elementdelivering energy.
 73. The system of claim 72 wherein the ablationcatheter further comprises a second ablation element for deliveringenergy to tissue.
 74. The system of claim 73 wherein the ablationcatheter is configured to monitor the temperature of the first ablationelement and the second ablation element.
 75. The system of claim 74wherein the higher of the first ablation element temperature and thesecond ablation element temperature is said at least one parametermonitored to prevent the energy delivered from exceeding said thresholdvalue.
 76. The system of claim 72 wherein the monitored parameter isselected from the group consisting of: temperature such as temperaturefrom a temperature sensor; a value of measured current; a value ofmeasured voltage; a flow measurement value; a force measurement valuesuch as a measurement of strain; a pressure measurement value; andcombinations thereof.
 77. The system of claim 72 wherein the energydelivery threshold is a peak energy delivered threshold.
 78. The systemof claim 77 wherein the threshold is 10 Watts.
 79. The system of claim72 wherein the energy delivery threshold is an average energy deliveredthreshold.
 80. The system of claim 79 wherein the threshold is 4 Watts.81. The system of claim 72 wherein the energy delivery threshold is acumulative energy delivered threshold.
 82. The system of claim 81wherein the threshold is 500 Watt-seconds.
 83. The system of claim 81wherein the threshold is 300 Watt-seconds.
 84. The system of claim 72further comprising a threshold comparator configured to compare adetermined value to a threshold.
 85. The system of claim 84 wherein saiddetermined value represents an instantaneous amount of energy deliveredto tissue.
 86. The system of claim 84 wherein said determined valuerepresents an integration of the amount of energy delivered to tissue.87. The system of claim 86 wherein the determined value can be reset.88. The system of claim 87 wherein the determined value is reset eachtime energy delivered to the at least one ablation element is switchedfrom off to on states.
 89. The system of claim 87 wherein the determinedvalue is reset each time the at least one ablation element isrepositioned by the operator.
 90. The system of claim 84 wherein saiddetermined value represents an average of the amount of energy deliveredto tissue.
 91. The system of claim 84 wherein the threshold comparatoris further configured to compare a second determined value to a secondthreshold.
 92. The system of claim 72 wherein said threshold valuechanges over time.
 93. The system of claim 72 wherein said system isconfigured to deliver a first energy level followed by a second energylevel, said first energy level of lesser magnitude than said secondenergy level.
 94. The system of claim 93 wherein said threshold ismodified after said first energy level is delivered.
 95. (canceled) 96.The system of claim 72 wherein the ablation catheter further comprises adeployable carrier assembly fixedly attached to a control shaft, saidcarrier assembly including at least one ablation element.
 97. The systemof claim 96 wherein the carrier assembly is flexible.
 98. The system ofclaim 97 wherein the carrier assembly is configured to conform with anendocardial surface of the heart.
 99. The system of claim 96 wherein theablation catheter further comprises a handle on its proximal end, saidhandle including means of deploying the catheter assembly. 100-101.(canceled)
 102. The system of claim 72 wherein the ablation catheterfurther comprises an integral functional element is selected from thegroup consisting of: a sensor; a transmitter; an imaging element; andcombinations thereof.
 103. The system of claim 102 wherein thefunctional element is a sensor selected from the group consisting of: anelectrical signal sensor such as a cardiac electrode; a temperaturesensor such as a thermocouple; an imaging transducer such as an array ofultrasound crystals; a pressure sensor; a pH sensor; a physiologicsensor such as a blood sensor; a respiratory sensor; an EEG sensor; apulse oximetry sensor; a blood glucose sensor; an impedance sensor; acontact sensor; a strain gauge; an acoustic sensor; and combinationsthereof.
 104. The system of claim 72 wherein the at least one ablationelement is an electrode. 105-110. (canceled)
 111. The system of claim 72wherein the at least one ablation element has a surface area less than2.5 mm².
 112. The system of claim 111 wherein the at least one ablationelement is configured to ablate tissue when energized with less than 10watts of energy. 113-116. (canceled)
 117. The system of claim 72 whereinthe at least one ablation element has a mass of less than 0.05 grams.118. The system of claim 117 wherein the at least one ablation elementis configured to ablate tissue when energized with less than 10 watts ofenergy.
 119. (canceled)
 120. The system of claim 72 wherein the at leastone ablation element has a volume of less than 3.0 mm³.
 121. The systemof claim 120 wherein the at least one ablation element is configured toablate tissue when energized with less than 10 watts of energy. 122.(canceled)
 123. The system of claim 72 wherein the at least one ablationelement comprises a thermally conductive portion configured to reside inor near circulating blood during the delivering of energy to tissue.124. The system of claim 123 wherein said at least one ablation elementhas a majority of its surface area in contact with circulating bloodduring the delivery of energy to tissue.
 125. The system of claim 123wherein said thermally conductive portion comprises a projecting fin.126-127. (canceled)
 128. The system of claim 123 wherein said thermallyconductive portion is configured to modify blood flow during thedelivery of energy to tissue.
 129. The system of claim 128 wherein saidthermally conductive portion is configured to change non-turbulent bloodflow to turbulent blood flow. 130-136. (canceled)
 137. The system ofclaim 72 wherein the at least one ablation element includes atemperature sensor.
 138. The system of claim 137 wherein the temperaturesensor is a thermocouple.
 139. The system of claim 72 wherein theablation catheter is configured to deliver multiple forms of energy.140-151. (canceled)
 152. The system of claim 72 wherein the deliveredenergy is selected from the group consisting of: sound energy such asacoustic energy and ultrasound energy; electromagnetic energy such aselectrical, magnetic, microwave and radiofrequency energies; thermalenergy such as heat and cryogenic energies; chemical energy; lightenergy such as infrared and visible light energies; mechanical energy;radiation; and combinations thereof.
 153. The system of claim 152wherein multiple forms of energy are delivered.
 154. (canceled)
 155. Thesystem of claim 152 wherein radiofrequency energy is delivered.
 156. Thesystem of claim 155 wherein monopolar and bipolar radiofrequency energyare delivered.
 157. The system of claim 156 wherein monopolar andbipolar energy are delivered sequentially.
 158. The system of claim 156wherein the power delivered to the at least one ablation element is lessthan ten watts.
 159. The system of claim 72 wherein the tissue iscardiac tissue.
 160. The system of claim 72 wherein the tissue isselected from the group consisting of: prostate; brain; gall bladder;uterus; tumor; and combinations thereof. 161-162. (canceled)
 163. Thesystem of claim 72 wherein the interface unit is configured to provideinformation relating to the temperature of the at least one ablationelement.
 164. The system of claim 163 wherein the information is rate ofcooling information.
 165. The system of claim 72 wherein the interfaceunit is configured to compare the temperature of the at least oneablation element to a threshold.
 166. The system of claim 165 whereinthe threshold is calculated by the system.
 167. The system of claim 165wherein the threshold is adjustable by the operator.
 168. The system ofclaim 165 wherein an ablation parameter is modified when said thresholdis reached.
 169. The system of claim 168 wherein modifying the ablationparameter results in a modification to the energy delivered to the atleast one ablation element.
 170. The system of claim 168 whereinmodifying the ablation parameter results in the activation of an alarm.173-175. (canceled)